Polycarbonate resins are resins that exhibit an excellent heat resistance and excellent mechanical and electrical properties and as a result are widely used as, for example, materials in the automotive sector, materials for electrical and electronic devices and equipment, materials for housing construction, and materials for the production of parts and components in other industrial sectors.
Within this sphere, flame-retardant polycarbonate resin compositions are advantageously used for components in, for example, information technology•mobile devices, e.g., computers, notebook computers, tablets, smart phones, and cell phones, and in office equipment, e.g., printers and copiers.
Electronic and electrical devices, and most prominently the information technology•mobile devices referenced above, have been getting smaller and thinner in recent years, and as a consequence there is demand that the materials used here be materials that, even in thin-wall configurations, are highly flame retardant and also exhibit an excellent rigidity.
Various strategies for increasing the rigidity of polycarbonate resins have been examined, and the strategy of incorporating a fibrous reinforcement, e.g., a glass fiber, is the most effective in responding to the demand for high rigidity for thin-wall configurations. The incorporation of a halogenated flame retardant in the polycarbonate resin has been used as means for imparting flame retardancy to such glass fiber-reinforced polycarbonate resins. However, polycarbonate resin compositions that incorporate a halogenated flame retardant, which contains chlorine or bromine, have been subject to a reduction in thermal stability and during molding operations have caused corrosion of the screw and molding tools in the molding equipment.
Glass fiber-reinforced polycarbonate resin compositions that incorporate an organophosphate ester are frequently used as an alternative strategy to the preceding (refer, for example, to Patent Documents 1 to 3).
However, it is difficult to respond to the recent requirements for thin-wall flame retardancy using resin compositions that incorporate an organophosphate ester flame retardant, and a drawback to such resin compositions has been that a substantial decline in the impact resistance and heat resistance occurs at the high levels of incorporation that will provide a high flame retardancy. In addition, due to the high specific gravity, it has not been possible with glass-reinforced polycarbonate resins to obtain the compact high-strength moldings that have come to be required in recent years.
In response to this, carbon fiber-reinforced polycarbonate resins that incorporate carbon fiber and organophosphate ester have been introduced (refer, for example, to Patent Documents 4 to 6).
However, a problem has been that such carbon fiber-reinforced polycarbonate resins still exhibit a reduced flame retardancy and heat resistance. Another problem has been that carbon fiber-blended polycarbonate resins also exhibit a substantial reduction in impact resistance.
Thus, while there has been strong demand for a polycarbonate resin composition that presents an excellent balance between the flame retardancy and the flowability, rigidity, impact resistance, and heat resistance, a resin composition having such properties has still not appeared.
In addition, a fatal drawback to the use of phosphazene compounds as flame retardants has been that they undergo consolidation or solidification upon exposure to compression or shear, and as a consequence, when they are blended into a thermoplastic resin by melt-mixing, the blend sticks or seizes and handling at an industrial level is thus quite problematic.
In order to solve this problem, a flame retardant masterbatch has been proposed in which a phosphazene compound is blended with a polyester resin, a polycarbonate resin, and a polyester elastomer (refer to Patent Document 7), and a flame retardant masterbatch formed of a phosphazene compound and a phenolic resin has also been proposed (refer to Patent Document 8).
However, the blending of such a flame retardant masterbatch into polycarbonate resin has not been able to effectively realize flame retardancy for the polycarbonate resin composition because the polyester elastomer and polyester resin, e.g., polyethylene terephthalate resin, or phenolic resin present in the flame retardant masterbatch cause a reduction in the flame retardancy.
In addition, since masterbatching by melt-mixing with a thermoplastic resin imposes a substantial thermal history, a problem has been that polycarbonate resin compositions that use a masterbatch undergo discoloration as a result.